The corpora allata (CA) of insects secrete juvenile hormone (JH) which profoundly affects development and reproduction. The long-term objective of the proposed research are to characterize the neurohormonal factors which regulate CA activity, to elucidate their modes of action, to identify the gene, and regulatory sequences (for the CA-regulating neurohormones) and to study the effects of external and internal stimuli on neurohormone production during critical periods of development. The tobacco hornworm (Manduca sexta), which is widely used as a model for neuroendocrinological, physiological and biochemical studies. will be used for the proposed studies. The focus of research will be allatinhibin (AI), a neurohormonal peptide which shuts down JH synthesis in the CA. The specific aims of this proposal are: a) to purify AI and to identify the amino acid sequence of AI, b) to develop a radioimmunoassay for AI and measure the hemolymph titer of AI-like activity during the larval pupal transformation, c) to identify AI- secreting neurons in the brain and examine the changes. in their secretory activity during development, and d) to study the action of AI on the CA. Surgical manipulation of the neuroendocrine system. in vitro - in vivo assay, and biochemical techniques will be employed in the investigations. These studies could have an important bearing on the development of novel chemicals for the control of insects which affect the health and economy of mankind.